Sample presentation geometries

FIGURE 4.2 Diffuse reflectance using a 0 to 45° sample presentation geometry. (Reprinted with permission from K. Norris, Reflectance Spectroscopy in Modem Methods of Food Analysis, AVI, Westport, CT, 1984.)... 

The flow system is an effective means of precise sample presentation to the detector. The detection unit contains a flow cell with a fixed location and orientation the handled sample is then always monitored with a fixed geometry. 

NIR analysis is directed to the determination of bulk properties and concentrations of the sample. In order to ensure precision of analysis, a sufficient number of particles must be present in the sample cell. Hirschfeld [37] discussed the relationship of measurement error as a function of sample area geometry and the average diameter of the particles. One effect of large particle size in a solid sampling diffuse reflectance cell is that the light penetration changes, distorting the spectrum. This is a known phenomenon in the visible-NIR [38,39],... 

In commercial thermoplastic rubbers, the endblock phase is present in the smaller proportion (see Table 2) and is dispersed in a continuous rubber matrix as suggested by Fig. 2. The uniform dispersion of spherical endblock domains shown in this figure, however, is approached only in carefully prepared laboratory samples with low endblock phase concentration. Depending on the endblock phase concentration and on actual processing conditions used to prepare a given sample, the geometry or morphology of the dispersed phase may be sphere-like, rod-like, or plate-like as depicted in Fig. 5. 

In Chapter 2, a brief discussion of statistical mechanics was presented. Statistical mechanics provides, in theory, a means for determining physical properties that are associated with not one molecule at one geometry, but rather, a macroscopic sample of the bulk liquid, solid, and so on. This is the net result of the properties of many molecules in many conformations, energy states, and the like. In practice, the difficult part of this process is not the statistical mechanics, but obtaining all the information about possible energy levels, conformations, and so on. Molecular dynamics (MD) and Monte Carlo (MC) simulations are two methods for obtaining this information... 

The data presented in Figure 19.7 were obtained on a Sonntag-Universal machine which flexes a beam in tension and compression. Whereas the acetal resin was subjected to stresses at 1800 cycles per minute at 75°F and at 100% RH, the nylons were cycled at only 1200 cycles per minute and had a moisture content of 2.5%. The polyethylene sample was also flexed at 1200 cycles per minute. Whilst the moisture content has not been found to be a significant factor it has been observed that the geometry of the test piece and, in particular, the presence of notches has a profound effect on the fatigue endurance limit. 

Because of the complexity of sample preparation, backscatter measurement geometry (see Fig. 3.19) is the choice for an in situ planetary Mossbauer instrument [36, 47 9]. No sample preparation is required, because the instmment is simply presented to the sample for analysis. On MER, the MIMOS II SH is mounted on a robotic arm that places it in physical contact with the analysis target (e.g., rock or soil) [36, 37]. 

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